Travail de fin d'études: Caractérisation de la dynamique environnementale au Sahel dans le contexte de la variabilité climatique à partir des indicateurs environnementaux dérivés l'imagerie satellitaire basse résolution : cas du Burkina Faso

Abstract

Burkina Faso, like the other countries of the Sahel, faces environmental issues partly linked to climatic and anthropogenic factors. Indeed, the strong climatic variability observed in this geographic area for decades combined with population growth and internal migrations generate a form of pressure on the environment leading to changes over time. Thus, for a better understanding and response to the various changes environmental factors, spatio-temporal monitoring of environmental dynamics is essential. This study falls within this framework. The overall objective is to contribute to a better characterization of environmental variability at the departmental scale in Burkina Faso over the past two decades (1999-2020) from environmental indicators derived from satellite imagery, namely the NDVI, with a view to identifying “potentially vulnerable areas”. To do this, CHIRPS rain data (precipitation estimates from rain gauges and satellite observations - resolution of about 4-5 km) and those of the Earth Observation System (SPOT - vegetation - spatial resolution of 1 km) covering all the departments over the period 1999-2020 were acquired, pre-processed and analyzed in the form of time series. The data extraction approach used at the level of the departments is that of the nearest neighbor (PPV) for the rain data and of the global average excluding land cover classes for the NDVI data. The analytical approach applied is that of a statistical approach based on the analysis of trends in the series. The water use efficiency (RUE) index and the Pearson correlation were used to analyze the relationships between rainfall and vegetation in the different zones. The results show that the rainfall and environmental dynamics in Burkina Faso were characterized by high variability with different trends. With regard to the rains, 95% of the localities experienced a progressive trend of rains with 45% of significant cases. On the vegetation side, a regressive change in plant cover was observed in 63% of the departments, including 14%, or 51 departments, which showed a significant trend at the 5% threshold of the Mann-Kendall test. These observed changes are partly due to anthropogenic pressure related to agricultural purposes. Indeed, the analysis of rainfall-NDVI relationships showed negative correlations (more than 50% of departments); as well as a downward trend in the RUE ratio. In contrast, agricultural statistics data in these areas showed an increase in sown agricultural areas during the 2010-2020 period of up to 50%, as in the provinces of Tapoa, Gourma, Banwa, etc. These results make it possible to understand the changes in the environmental dynamics in Burkina Faso of the latter. They can serve as a basis for a more in-depth study with a view to planning a more rational response and management to this environmental risk, namely the degradation of the vegetation cover